(a) Field of the invention:
This invention relates to electric shutter mechanisms and more particularly to improvements in a cocking mechanism for electric local plane shutters. (b) Description of the Prior Art:
Conventional electric focal plane shutters may be divided broadly into (a) a type wherein the front shutter blade is mechanically controlled and the rear shutter blade is controlled by an electromagnet and (b) another type wherein each of the front and rear shutter blades is controlled by an electromagnet. Further, the shutters of the above mentioned type (b) may be divided into (c) a type wherein the front and rear shutter blades are controlled by a single electromagnet and (d) another type wherein the front and rear shutter blades are controlled respectively by two independent electromagnets. Still further, the shutters of the above mentioned type (d) may be divided into (e) a type wherein the shutter blade driving means are released by energizing the electromagnet including a permanent magnet so that the resultant magnetic field becomes nil and (f) another type wherein the shutter blade driving means are released by energizing the electromagnet to produce an attractive force.
The structural features of conventional electric focal plane shutters may be different from one another due to the type of the electromagnet to be used. Accordingly, the type of the electromagnet to be used is selected in accordance with the purpose of use of the camera.
However, there is not yet suggested an electric focal plane shutter of the above mentioned type (f) wherein an armature lever is released when an electromagnet is de-energized, the lock of the blade driving means is released by the said action of the armature lever and the armature lever is pressed against the electromagnet while resisting a spring force by the shutter cocking operation. In such an electric focal plane shutter in which the shutter cocked state is held by the attraction of the electromagnet, there will be required a cocking member for bringing the armature lever to the cocked position from an uncocked position and a holding member for pressing the armature lever against the electromagnet in the cocked state until the electromagnet is energized. This holding member must be retreated out of the moving track of the armature lever before the electromagnet is again de-energized. Therefore, in an electric focal plane shutter of a type of controlling the shutter opening and closing with the cooperation of the electromagnet and armature lever, a cocking member and holding member will be required for each armature lever and each holding member must be moved as mentioned above. This fact not only complicates the shutter mechanism but is also likely to cause a misoperation. It is likely to be influenced by errors in working and assembling parts and has been often possible to fail.